U.S. patent application Ser. No. 718,409, filed Apr. 1, 1985, entitled "Circuit Breaker Assembly For High Speed Manufacture" describes a circuit breaker manufactured, in part, by automated processing equipment. The breaker operating mechanism allows a uniform breaker design to be operative over a wide range of breaker ampere ratings. A removable trip unit assembly facilitates the insertion of selected trip elements for breakers having progressively higher ampere ratings. It has since been determined, that a single thermal element design can be used for various ampere ratings by controlling the thermal response of the thermal element by means of rating plugs having predetermined thermal load characteristics.
One example of an earlier rating plug design is found within U.S. Pat. No. 2,831,935 in the name of Robert G. Paige, which describes a combination circuit breaker and motor starter device that changes the ampere rating of the device by changing the size of the resistance heater used to replicate the electrical current flow through the protected circuit. The thermally responsive trip element responds to the predetermined temperature values set by each of the resistance values. This arrangement allows a single circuit breaker design to operate over a range of breaker ampere ratings by proper selection of the resistance values.
An additional circuit breaker design having variable ampere ratings is found within U.S. Pat. No. 2,839,633, which issued to David F. Moyer. This patent discloses the use of a rating plug in the form of a spring-loaded heat absorbing mass. The thermal input to the circuit breaker bimetal trip element is varied by increasing or decreasing the size of the heat absorbing mass.
U.S. Pat. No. 4,570,144, which issued to Robert B. Bridges et al., describes a thermally actuated variable-rating circuit breaker including an adjustable heat sink element to effectively vary the ampere rating of the breaker.
The instant invention proposes a selectable rating plug for setting the ampere ratings of a molded case circuit breaker by the arrangement of materials of predetermined thermal diffusivities in thermal relation with the thermally responsive trip element in correspondence with the tripping requirements for each ampere rating.